the Laws of Affinity \ 13* 



difcover, in the precipitation of the mercury, filver, gold, and 

 topper, in the metallic ftate, the influence of thefe two forces^ 

 that is to fay, the mutual affinity of the particles of one and 

 the lame metal, and the affinity of one metal for another. 



4. When a piece of copper is put id a foiution of mercury 

 in nitric or in muriatic acid, the capper hecomes iultantly 

 white, arid the mercury is revived, but combined with the 

 copper. If, inftead of copper, a plate of clean iron be plunged 

 ih the fame folution, after feveral hours the liquid appears 

 tlifturbed, and at length a precipitate Is formed ; but with the 

 muriatic folution in particular, this precipitate is partly in the 

 itate of an oxide, and very probably retains a portion of acid. 



If the affinity of one metal for oxygen were the fole caufe 

 that produced the precipitation of another metal, the iron 

 ought to ad with greater efficacy than the copper) for it is 

 known to have a ftronger affinity for oxygen: but its action 

 is (low, difficulty and incomplete, While that of copper is in- 

 itantaneous. It is feen by the manner in which the inde- 

 compofable acids are retained by the oxide of copper and the 

 oxide of iron, when thefe combinations are expofed to the 

 action of heat, that there can only be a very fmall difference 

 between the affinities of thefe metals for the acids. There is 

 confeqtiently no doubt that the affinity of the copper for the 

 mercury, with which it has actually combined, mud have 

 greatly contributed to its precipitation in the metallic ftate; 

 but in the experiment with iron, the mutual affinity of the 

 particles of mercury muft alone have decided, though with, 

 difficulty, the reduction of the mercury *, a portion was alfo 

 precipitated in oxide, and probably retained a portion of acid, 

 as the whole would have done, if the affinity of the iron for 

 oxygen had been the fole agent ; and the portion precipitated 

 in the metallic ftate did not combine with the iron. 



5. If a folution of filver be precipitated by copper, the pre- 

 cipitate, which is in the metallic ftate, is not pure filver, but 

 a combination of filver with a fmall portion of copper: it 

 could not take the copper from the plate itfelf, which waa 

 plunged in the folution ; it muft therefore have precipitated 

 with it out of the folution: the mutual affinity of thefe two 

 metals decides their deoxygenation. By means of this force, 

 two combinations are effected, as often happens : one, that 

 of the acid with the oxide of copper 5 the other, that of the 

 filver with a portion of the copper. The a£tion of the acid 

 upon the oxide of copper, and that of filver upon copper, am 

 thus put in equilibrio. 



6. In like manner, if a plate of copper be plunged into 2L 

 folution of gold, the gold which is precipitated, mows, by its 



I % deeper 



